1. Field of the Invention 
The present invention relates to a latching mechanism for an access lid to a subsurface chamber for servicing aircraft. 
2. Description of the Prior Art 
At modern aircraft terminals the servicing of aircraft on the ground is frequently performed using subsurface pits, which are often prefabricated structures. Such aircraft servicing pits are installed at aircraft docking, fueling, and loading areas beneath the  surface of the tarmac across which aircraft travel during docking and departure maneuvers. The pits form a subsurface chambers and are typically constructed of fiberglass, steel, concrete, or aluminum. These pits are often constructed as complete enclosures with surrounding walls, a floor, and an access lid at the top seated within a frame disposed about the neck of the prefabricated pit. When the lid is closed it lies substantially flush with the surface of the tarmac. Such pits are installed below the surface of loading and refueling aprons at aircraft terminals, remote parking locations, and aircraft maintenance bases. 
The purpose of the pits is to allow ground support functions to be carried out from subsurface enclosures. These ground support functions include the provision of fuel, the provision of electricity to an aircraft while it is in the docking area, the provision of air for cooling the aircraft interior, the provision of pressurized air for starting the aircraft engines, and for other aircraft support activities on the ground. The use of subsurface pits eliminates the need for mobile trucks, carts, and other vehicles which are otherwise present in the loading area and which interfere with each other and with the arrival and departure of aircraft in the vicinity of a loading gate. 
The use of subsurface pits also allows the provision of fuel, power, cooling and pressurized air, and other supplies from a central location. The necessary fluid supplies and electrical power can be generated or stored with a greater efficiency at a central location, as contrasted with mobile generating or supply vehicles. 
The pits located below the aircraft terminal area house valves, junction boxes,  cooling air terminations, and other terminal equipment that is temporarily connected to an aircraft that has been docked. Umbilical pipes and lines, otherwise housed within the pits, are withdrawn from them through hatches therein and are coupled to a docked aircraft to supply it with fuel, air for cooling the aircraft interior, pressurized air for starting the engines, and electrical power. 
The pits are constructed with either hinged or totally removable lids that can be moved between open positions allowing access to the pits and closed positions which are flush with the surfaces of the docking, loading, or refueling areas across which aircraft travel and beneath which the pits are mounted. To ensure that the pit lids remain flush with the surrounding surfaces, it is desirable to employ a latching mechanism. Very typically such a latching mechanism involves a catch depending from the underside of the edge of the pit lid remote from the hinge about which the pit lid is rotatably mounted to its surrounding frame. The catch engages a latch bar secured to the interior wall of the pit. The catch is normally moved in rotation about a horizontal axis by means of a lever arm located in a cavity at the underside of the pit lid remote from the axis at which the pit lid is mounted to the frame. Access to the latch actuating mechanism to operate the lever arm is normally provided in a handgrip pocket cavity in the upper surface of the pit lid. 
To open the pit lid the user inserts the fingers of one hand into the cavity in the pit lid. The user then presses upwardly on the latch actuating mechanism, thereby rotating the lever arm. The lever arm and catch mechanism operate in the manner of a  bell crank, so that rotation of the latching mechanism lever arm pulls the catch from beneath the latch bar and allows the user to open the pit lid. One prior mechanism of this type is described in U.S. Pat. No. 4,739,896, which is hereby incorporated by reference in its entirety. 
In some circumstances pits without latching mechanisms have been installed beneath docking and undocking locations as air terminals. However, it has subsequently been determined that some type of positive latching mechanism is either necessary or highly desirable at such locations. Latch mechanisms typically require a particular type of configuration of the pit lid when the pit lid is initially fabricated. However, once the pit lid has been installed, it has been quite difficult to retrofit the pit lid with a latch mechanism since pit lids without latch mechanisms typically have different configurations than pit lids originally designed to be equipped with latch mechanisms. 
Many conventional pit latching systems require one or more of the latch mechanism components to be mounted on the interior wall of the buried pit. However, in subsurface aircraft serving pits originally designed to be used without a latch mechanism there is often equipment or other structure already in the pit, either at the location at which the internally mounted latch component would have to be installed or in such a location as to obstruct installation of the necessary component. In either case, it is often extremely difficult, if not impossible to retrofit existing pits with conventional pit latching mechanisms.  